The present invention relates to masks for use in manufacturing devices such as semiconductor integrated circuits and the like, and more particularly relates to such masks having patterns thereon that are compensated in a way that allows for optimized images of the patterns to be printed.
Modern day semiconductor devices, such as integrated circuits and the like, are fabricated using photolithographic processes. In a typical photolithographic process, light from an illumination system is passed through a mask having a pattern. The mask is typically a glass substrate, and the pattern is typically opaque and is formed from a metal such as chrome. The light passing through the mask is imaged by a projection optical system onto a wafer coated with a photosensitive material (e.g., photoresist). The mask pattern is thus recorded in the photoresist, and is subsequently developed, thus forming a resist pattern. The resist pattern is then transferred into the wafer by various known deposition, etching and other processes. This process is repeated for various types of masks to form a layered structure in the wafer, ultimately forming a semiconductor device.
In the above process, the pattern on the mask often has a size that is at the resolution limit of the projection optical system. In such a case, though the patterns may have similar dimensions on the mask, diffraction from the mask and the limited aperture of the lens result in the photoresist pattern having a different size. A well-known example of this phenomenon is the problem of isolated patterns printing larger than nested patterns of the same size. This size differential creates problems in obtaining functional devices, since it is difficult to choose the proper exposure for obtaining linewidths that are within the device specifications.
There are a variety of known techniques for compensating mask patterns so that the corresponding resist patterns print in a desired manner. For example, U.S. Pat. No. 5,827,623 discloses a half-tone phase-shift mask designed to compensate for proximity effects. Also, U.S. Pat. No. 5,242,770 discloses a mask for photolithography that reduces proximity effects by having xe2x80x9cintensity leveling bars,xe2x80x9d i.e., lines less than the resolution limit of the projection optical system, arranged adjacent the isolated edges of a mask pattern so as to make the isolated feature have the same intensity profile as nested features. However, each of the above-mentioned prior art masks are complicated and costly to manufacture, and do not always produce the desired results.
The present invention relates to masks for use in manufacturing devices such as semiconductor integrated circuits and the like, and more particularly relates to such masks having patterns thereon that are compensated in a way that allows for optimized images of the patterns to be printed.
A first aspect of the invention is a method of making a mask that is compensated to allow for optimized images of patterns thereon to be formed on a photosensitive substrate. The method involves providing a substrate transparent to light of a first wavelength. The substrate has an upper surface on which is formed (i) a first segment having first sidewalls, and (ii) a second segment having second sidewalls. Next, a conformal layer is deposited atop the upper surface so as to conformally cover the first segment and the second segment. Finally, the conformal layer is removed so as to leave a partial conformal layer surrounding the first segment. The partial conformal layer extends outwardly from the first sidewalls a distance d, as measured in a direction parallel to the upper surface.
A second aspect of the invention is a method of making a mask that is compensated to allow for optimized images of patterns thereon to be printed on a photosensitive substrate. The method involves providing a substrate transparent to light of a first wavelength. The substrate has an upper surface on which is formed (i) a first segment having first sidewalls and (ii) a second segment having second sidewalls. Next, a conformal layer is deposited so as to conformally cover the first segment and the second segment. Then, portions of the conformal layer are removed so as to provide first spacers adjacent the first sidewalls and second spacers adjacent the second sidewalls. Finally, the second spacers are removed from the second sidewalls.
A third aspect of the invention is a mask compensated for optimized imaging of first and second patterns. The mask comprises an upper surface having first patterns, each comprising a first segment having first sidewalls, and second patterns, each comprising a second segment having second sidewalls. The mask also includes spacers adjacent the first sidewalls of the first segments and extending a distance d from the first sidewalls of the first segment.